The amplification of Estrogen, Progesterone and Human Epidermal Growth Factor receptors (i.e. ER, PR and HER2) serve as prognostic markers in breast cancer. The prognosis of ER+ breast cancer is relatively better due to availability of several drugs that essentially block ER-signaling. However, HER2+ breast cancer has limited options and is treated either by using humanized antibodies, Trastuzumab (Herceptin) or Pertuzumab or tyrosine kinase inhibitor, Lapatinib. The initial responses to anti-HER2 therapies are favorable, however, the tumors subsequently acquire resistance and relapse to form metastatic tumors. Therefore, there is a need to identify novel target and develop new therapeutics that can overcome anti-HER2 therapies resistance and perhaps can be used as an alternative to the existing anti-HER2 agents. Interestingly, it is well recognized that HER family-mediated signaling primarily impinge on PI3K-AKT pathway and is reported to be a main source of either, de novo or acquired resistance. Therefore several inhibitors of PI3K or AKT have been in clinical trials, however the outcome of these trials are dismal due to unacceptable toxicities. Furthermore, it is also reported that ER and IGF1R are co-amplified in HER2 positive tumors, treated with anti-HER2 therapies, leading to resistance. Both of these receptors are known to activate PI3K-AKT and is considered to be initiating anti-HER2 therapies resistance. Collectively these results suggest that PI3K-AKT is one of the main nodal point of resistance in HER2+ tumors. Therefore, any therapeutic(s) that can block PI3K-AKT signaling pathway and congruently also activate the downstream pro-apoptotic molecule will be a drug of choice to treat both HER2 therapy sensitive and resistant tumors. We reported previously that a member of Mixed Lineage Kinase (MLK) family, MLK3 was inhibited by ER, IGF1R and HER2 pathways and this inhibition was mediated via direct phosphorylation of MLK3 by AKT. We also reported that ceramide, a bioactive lipid was able to activate MLK3 and was necessary for MLK3-mediated cell death. It is reported that ceramides inactivate PI3K-AKT pathway and therefore we hypothesize that delivery of ceramides into HER2-resistant and sensitive cells might cause cell death and tumor regression. Our preliminary data clearly showed that indeed ceramide nanoparticles were able to cause cell cycle arrest and cell death in Herceptin resistant cell lines and xenografts. Based on our intriguing results, we hypothesize that ceramide nanoparticles could be a better option to treat both HER2 resistance and sensitive tumors. To determine the effectiveness of ceramide nanoparticle as an alternative option to treat both resistant and sensitive HER2+ breast cancer, we will determine: 1) the effects of ceramide nanoparticles on cell lines- and xenografts-resistant to anti-HER2 therapies, 2) the molecular mechanisms of anti-tumorigenic effects of ceramide nanoparticles in HER2+ breast cancer and finally, 3) the therapeutic efficacy of ceramide nanoparticles in HER2 transgenic and PDX animal models, resistant to anti-HER2 therapies. It is expected that at the conclusion of this project we would discern the therapeutic value of ceramide nanoparticles in treating HER2 resistant and sensitive breast cancer, and perhaps other sub-types. It is important to note that it is reported that ceramides damage specifically tumor but not normal cells and therefore we expect that our results will provide an innocuous therapeutic to treat HER2+ breast cancer with minimal, or no collateral damage.